The subject of this invention is an aerodynamic and spatial mixed flight aircraft, and the related piloting method thereof.
The field of the invention is that of spaceplanes, i.e. vehicles capable of taking off from the ground like aircraft, reaching space and returning by landing on Earth, also like aircraft. These vehicles must be able to carry a payload and offer suitable safety conditions for manned flights, like conventional aircraft, and they must in particular be reusable, unlike rockets, which are consumed during the launch at the end of the flight. The term space may be understood according to International Aeronautical Federation terminology, which refers to the entire designated volume outside the Earth's atmosphere, above one hundred kilometers in altitude by convention. It may also be considered as the volume where the atmosphere is too rarefied to enable the flight of conventional aircraft.
A distinction may be made between orbital aircraft, which are capable of reaching the orbital speed at a given altitude (of the order of 7.5 km/s at 200 km in altitude), and suborbital aircraft, which are unable to do so. Orbital aircraft are capable of becoming satellites remaining for an almost indefinite time in orbit after the propulsion phase, whereas suborbital aircraft follow a trajectory which returns them to Earth when the propulsion phase thereof is complete, after a finite time, of the order of an hour and a half, or less. Orbital aircraft are distinguished from suborbital aircraft particularly by the quantity of energy to be carried to reach the orbital speed and by the specific design received to withstand the considerably greater overheating experienced on re-entering the atmosphere. The present invention firstly relates to suborbital aircraft, but not exclusively since it would be conceivable to apply it to orbital aircraft with quantitative or secondary modifications, and it may also transport a vehicle capable of orbital flight as its payload.
Unlike rockets which have already been the subject of significant industrial developments, spaceplanes are still very infrequent, and many only exist in the project phase. A first example is the American shuttle which is not, however, a spaceplane per se but a two-stage composite launcher, taking off like a rocket and wherein only the second stage, which is released after the takeoff phase, is a space glider. This space glider has the dual advantage, sought with the invention, of being able to be reused and land on Earth in the same way as a supersonic glider, therefore at a high speed and without being able to correct an error; however, the first stage retains the drawbacks of the rocket, primarily the single use and the high consumption of propellant or fuel to pull away from the near atmosphere.
A second example of a spaceplane was devised by Scaled Composite; it also has two stages. A first aerodynamic flight aircraft pulls another to around 15 km in altitude and releases it. The second aircraft has an anaerobic rocket engine, capable of carrying the payload to 100 km in altitude. Said second stage lands similarly to that of the shuttle.
A third, substantially older, example, is the American X15 prototype, which was released from a carrier aircraft and could reach an altitude greater than 100 km.
Other space vehicles are described in the website http://www.spacefuture.com/vehicles/designs.shtml, but these vehicles have not been built or commissioned. Some take off vertically, but their propulsion mode remains as costly as that of a rocket, or they are associated with a rocket serving as a first stage thereof, such as the American space shuttle.
The documents EP 0 264 030, GB 2 362 145, WO 98/30 449, WO01/64513, U.S. Pat. No. 6,119,985, U.S. Pat. No. 6,745,979, US 2005/0279889, U.S. Pat. No. 6,193,187 and FR 1 409 570 respectively illustrate a two-stage launcher; a launcher wherein a balloon is the first stage; an aircraft pulling another; a launcher wherein the first stage is a composite propulsion launcher for aeronautical engines and rocket engines; a spacecraft fuelled with oxygen; three variable geometry aircraft; and a conventional aircraft (with a propeller in the embodiment shown) whereto orientation modification nozzles have been adjoined, which are auxiliary engines not involved in propulsion.
Therefore, the majority of aircraft projects in space, and the only ones to have flown have multiple stages. This design appears to be more advantageous in that it allows a more beneficial ratio between the effective mass and the mass at takeoff, which offers the possibility of associating a greater quantity of fuel with the payload and therefore propel same further. The drawbacks are that the complexity is increased considerably and that the upper stage has reduced scope for movement. The two stages must all be equipped with the same means for some functions, such as the directional nozzles to adjust the orientation thereof and they must also comprise separation means. The upper stage is not piloted effectively for the return and must re-enter in glide mode. This and the circumstance that the release means may be subject to failures renders the flight more risky.
Some aircraft used composite aerobic and anaerobic propulsion, to circulate successively in the dense atmosphere and in space. This idea is used in the invention, more effectively however as prior designs do not generally make it possible to do away with the constraint of multiple stages. The main reason lies in a different choice of wings, as it appeared to the present inventors that the wings generally proposed for said prior designs were short, delta-shaped wings with a large back-sweep, well-suited to supersonic flights but wherein the lift is less satisfactory. On the other hand, the design according to the invention uses a long, straight wing, with a small back-sweep, to provide a satisfactory lift in the dense atmosphere and up to a high altitude. These portions of the voyage are completed without problems at subsonic speed. The rocket propulsion only starts at a relatively high atmosphere so that the aerodynamic forces remain manageable for the wing. In this case, it is not necessary to adopt a variable geometry to protect the wing and reduce the drag by folding it back against the fuselage.
On the contrary, a rigid, simpler, lighter design is preferred, requiring less maintenance and not subject to damage.